1. Field of the Invention
The invention relates to a process for the preparation of macrocyclic, preferably from 12- to 20-membered, esters of the general formula (I): ##STR1## in which m is an integer from 6 to 14 and n is an integer from 2 to 12, from dicarboxylic acid glycol esters of the general formulae:
formula (II) HO--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO--O--(CH.sub.2).sub.n --OH; PA1 formula (III) H{O--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO}.sub.x --O--(CH.sub.2)n--OH; PA1 formula (IV) H{O--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO--}.sub.x --OH; and/or PA1 formula (V) HO--CO--(CH.sub.2).sub.m --CO--{--O--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO--}.sub.x --OH, PA1 formula (I): I HO--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO--O--(CH.sub.2).sub.n --OH; PA1 formula (III): H{O--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO}.sub.x --O--(CH.sub.2)n--OH; PA1 formula (IV): H{O--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO--}.sub.x --OH; and/or PA1 formula (V): HO--CO--(CH.sub.2).sub.m --CO--{--O--(CH.sub.2).sub.n --O--CO--(CH.sub.2).sub.m --CO--}.sub.x --OH,
in which m and n are as defined above and x is an integer &gt;1, preferably from 2 to 10.
Cyclic esters of this type and in particular the cyclic ethylene brassylate, formed from the monomeric units brassylic acid and ethylene glycol, are extremely important in the perfume industry as a constituent of perfumes having an ambergris or musk note or as a fixative in fragrance mixtures.
2. Discussion of the Related Art
It is known to obtain macrocyclic esters by cyclizing depolymerization of oligomeric or polymeric glycol esters of corresponding carboxylic acids. The depolymerization is normally carried out at high temperatures and under reduced pressure in such a way that the resulting target products can be distilled off and obtained by condensation. The cyclizing depolymerization is described, for example, in J. Am. Chem. Soc. 57 (1935), 929-34 and U.S. Pat. No. 4,175,321.
It is further disclosed in U.S. Pat. No. 4,709,058, JA-B 55-120 581 and DE 32 25 341, that the preparation of macrocyclic esters by cyclizing depolymerization is advantageously carried out using inert high-boiling reaction media. A significant problem with any cyclizing depolymerization is that, under the reaction conditions, it is also possible for relatively high molecular weight esters to form through polycondensation of oligomers or polymers having terminal carboxyl groups with other oligomers or polymers which carry terminal hydroxyl groups, with the elimination of water, or through polycondensation of oligomers or polymers having terminal hydroxyalkyl groups with the elimination of glycol. The desired intramolecular formation of the macrocyclic monomeric target products is thus accompanied by an undesired intermolecular formation of linear, unreactive highly polymeric esters. However, this not only reduces the yield of the intended product, but also causes considerable process engineering problems.